Mildew-resistant mineral-coated soap wrap



Patented Dec. 8, 1953 UNITED STATES PATENT 01 F101:

Joseph J. Thomas, Westbrook, Maine, assignor to S. D. Warren Company,Boston, Mass., a corporation of Massachusetts No Drawing. ApplicationAugust 17,1949, Serial No. 110,881

7 Claims. (01. 117*155) This invention relates to a mildew-resistant Imineral coated paper product suitable for use in Wrapping cakes of soap.I

Soap is customarily made by reacting an alkaline reacting, alkali-metalcompound, e. g. sodium hydroxide or sodium carbonate, with a suitablefat or suitable fatty acid in aqueous medium. The soap so formed isseparated from the mixture, as by salting out, and if desired othermaterials may be added thereto, e. g. 001- oring or perfuming materials.The soap is then pressed into bars or cakes which are usually wrappedindividually in paper wrappers before being stored.

Soap usually, and probably always, contains a considerable amount ofwater at the time it is pressed into cakes and wrapped. While some ofthe water content is doubtless lost during prolonged storage,nevertheless s'ufiicient moisture remains for a comparatively long timeso that the paper wrapper for a considerable period is kept somewhatdamp and slightly alkaline by reason of the alkalinity of the soapdissolved by the water. Consequently conditions are favorable fordiscoloration of the paper wrapper by alkali and for development ofmildew or mold on or in the wrapper because of its damp and alkalinecondition.

Obviously neither alkali-stain nor mildew can be tolerated in thewrapper of an article offered for sale. Various suggestions have beenmade in regard to prevention of alkali staining of uncoated paper soapwrappers; for example, to use only high-alpha cellulose fiber; to avoiduse of rosin size; and to include acid in the paper. a

it has never been considered safe to wrap any of the largest sellingbrands of soap in mineralcoated paper. Mineral-coated papers have tra=ditionally been made by applying to a suitable paper base or body stockan aqueous slurry comprising mineral pigment such as clay, calciumcarbonate, or titanium dioxide, and adhesive material, usually casein,glue, or starch, and drying the so coated paper. It has been found thatthe adhesives commonly used in most min 2 eral coatings for paperprovide a medium highly favorable for the development of the molds whichproduce mildew. In fact such conventional adhesive materials supportmold growth so much more efiectively than does cellulose that it is notpracticable in the case of coated soap wrap paper containing suchadhesives to use sufficient mold inhibitor to prevent mold growththereon. To make such paper moldproof requires such excessive amounts ofmoldinhibitor that the resulting product is objectionable fromconsideration of odor and/or toxicity.

Practice of the present invention yields a satisfactory mineral-coatedsoap-*wrap paper which is capable of being printed satisfactorily, whichis satisfactorily alkali-proof, and which is free of mold-nutrientmaterial at least as resistant to mold or mildew as are usual uncoatedsoap- Wrap papers.

According to the invention, a paper web of any desired weight isprepared from a furnish comprising bleached chemical wood pulp which isof high quality, but not necessarily of the highest quality high-alphafiber. The furnish may contain filler, if desired, such as clay orcalcium carbonate, and may be sized with rosin size, but it should notcontain starch, casein or other substance which readily supports moldgrowth. The paper web is then coated, preferably on one side only, byany desired method, with an aqueous mineral-coating composition which isfree from the natural adhesive materials aforesaid which mold so easily.Instead, the composition is made up of mineral matter such as clay,calcium carbonate, titanium oxide, or the like and an adhesivecomprising synthetic material which is not readily attacked by thecommon molds which cause mildew. The coated paper is dried and smoothedin known fashion. It is then usually printed, and finally it is used towrap a somewhat moist cake of soap. The wrapped cakes of soap may bestored for a considerable time. It is found that packages so preparedshow no more tendency to develop mildew or alkali-stain than similarpackages in which an uncoated paper wrap is used. 'That is to say, underordinary storage conditions no trouble whatever occurs from mildew oralkali-stain. It is to be understood, of course, that neither type ofpackage, either the one wrapped in uncoated paper or the improvedpackage of the invention wrapped in mold-resistant mineral-coated papercontaining only synthetic adhesive, is intended to withstand immersionin water or actual condensation of a visible film of water on-itssurface.

*Several synthetic adhesive materials are available which are certainlyas mold-resistant as cellulose fiber, and in some cases are considerablymore mold-resistant. While generally speaking any such material may beused as adhesive in a mold-resistant coating, adhesives of the classknown to the trade as synthetic elastomers are extremely usefula typicalsynthetic elastomer being the common styrene-butadiene copolymer usuallycalled GRr-S rubber. The elastomers are used as coating adhesives in theform of an aqueous dispersion, commonly referred to as a latex fromanalogy with natural rubber latex.

While it is possible to use such a synthetic elastomer latex as the soleadhesive component in a mineral coating, the coating composition is mademuch more stable by inclusion therein of a protective colloidalmaterial. It has been found that synthetic protective agents can be usedin this relation with good results. For example, polyvinyl alcohol canbe used effectively to protect the synthetic elastomer in the coatingcomposition. Other suitable protective agents include methyl cellulose,carboxymethylcellulose, hydroxyethyl cellulose. Obviously, for thereasons previously stated, such known natural proteotive colloidalmaterials as casein, starch or glue cannot be used as protective agentsfor the synthetic elastomers employed in the mineral coating compositioncontemplated herein.

Suitable synthetic elastomers include styrenebutadiene copclymerstypified by GR-S rubber, butadiene-acrylonitrile copolyrners,styrene-isoprene copolymers, methyl acrylate-acrylonitrile copolymers,polychloroprene, plasticized polystyrene. plasticized polyvinylchloride, and plasticized copolymer of vinyl chloride and vinylidenechloride. Any of such synthetic elastomers or any of the protectiveagents mentioned in the preceding paragraph can be used as the soleadhesive in a mineral-coating composition according to the invention,but the preferred practice is to use a mixture of a synthetic elastomerand a synthetic protective colloid of the type mentioned previously.

Owing to the before-mentioned necessity for exclusion from the paperbase of substances which actively support mold growth, it is practicallyessential under the invention to restrict the fiber content to new orsocalled virgin fiber. That is because of the practical impossibility ofbeing certain that any specific lot of reworked or old paper pulp ismade from papers entirely free from mold-promoting substances. Avoidanceof old paper pulp does not, of course, preclude the reuse of trimmingsand broke made duringthe actual manufacture of the paper described.Naturally such material is recycled through the paper making process andis the full equivalent of the original virgin fibers.

Of the synthetic elastcmer latexes available, consideration of costtends to narrow the choice for the paper coating field to thestyrene-butadiene copolyrhers, that is to the GR-S type of latex. Someoi the other synthetic elastomers mentioned are actually somewhatsuperior in their physical qualities to GR-S latex, but their presenthigher price discourages their replacing the relatively cheap GRPSlatex. The GR-S type latex is quite satisfactory as a paper-coatingadhesive, the 60 styrene-40 butadiene copolymer being one which isespecially good for such use.

When only a small quantity of synthetic protective colloid is used toprotect the latex it makes 4 little difference which one is used.Polyvinyl alcohol is very satisfactory for this purpose, and when alarge quantity of colloid is desired to be used with the latex,polyvinyl alcohol is probably the most convenient to use.

The coating compositions of the invention appear to be somewhat lesssusceptible to mold growth than is ordinary unccated paper made frompurified cellulose fiber without addition of natural organic matter suchas starch, casein, etc. In fact the coating of the invention probably tosome extent acts actually to increase the mildew-resistance of papercoated therewith. Nevertheless, some users may prefer to include in thecoating an unobjectionably small but effective quantity of mold-proofingagent equivalent to that frequently used in uncoated paper soapwrapper.For example, about 0.5% of Preventol G. D. may be included in thecoating, Preventol G. D. being the trade designation of a moldinhibitorconsisting essentially of the organic chemical2,2-dihydr0xy-5,5-dichlcrodiphenylmethane. Tests have not shown theinclusion of such an agent to be necessary in practicing the invention,but such an addition does probably give an increased factor of safety.It may be said that addition of that quantity of mold-inhibitor to anordinary casein-containing mineral coating for paper is not effective toprevent mold-growth in paper coated therewith and subsequently used as asoap-wrap.

Following are examples of mineral coated papers according to theinvention:

Example 1 A paper making furnish was prepared from about equalquantities of bleached sulfiite pulp and bleached soda pulp. Added tothis were rosin-size, alum, and clay filler. The furnish was formed intoa paper web and dried. The paper so made contained 8 per cent of clayand weighed 48 pounds on the basis of 500- sheets 25 X 38 inches insize. The paper web wa then coated on one side with 12 pounds, dryweight per ream, of a coating composition consisting (in addition towater) of:

parts coating clay 0.5 part tetrasodium pyrophosphate (a dispersingagent) 0.5 part low viscosity polyvinyl alcohol 16 parts (dry basis) ofa 60-64 styrene-butadiene copolymer 2 parts tributyl phosphate (ananti-ioaming agent) Example 2 The experiment described in Example 1above was repeated, but there was added to the coating composition 0.4part of a mold inhibitor, Preventol G, 1). consisting essentially of2,2'-dihydroxy-5,5'-dichlorodiphenylmethane.

Example 3 A paper web was made from a furnish containing 60 parts orgood quality bleached wood fibers, from coniferous trees, prepared bythe sulfite pulping process and so parts of good quality bleached woodfibers, from deciduous trees, prepared by the soda pulping process. Thefurnish was sized with rosin-size and alum, and contained no filler, nowaste paper, and no added mold-supporting organic matter. The weight ofthe paper web was 43 pounds on the basis of a 500 sheet ream 25 x 38inches in size. The paper web was coated on one side by means of aWarren air-knife coater with 17 pounds dry weight per ream of a coatingcomposition containing (in addition to water) the following ingredients:

100 parts high quality calcium carbonate 0.5 part tetrasodiumpyrophosphate 0.5 part low viscosity polyvinyl alcohol 20 parts (drybasis) 60-40 styrene-butadiene copolymer 2 parts tributyl phosphateExample 4 The experiment described in Example 3 above was repeated, butthere was added to the coating composition 0.4 part of Preventol G. D.

The sheets of all four examples were supercalendered to a high finish,printed with appropriate indicia, and used to wrap cakes of freshly madesoap of about 30 per cent moisture content. The wrapped cakes werepacked in cartons as is customary, and were stored for several monthsunder storage conditions normally conducive to mold formation, N0 mildewdeveloped in any case and all samples were considered satisfactory.

The term mineral-coated paper as used herein refers to paper having asupercalendered surface layer'consisting essentially of a majorproportion of finely divided mineral matter, i. e., pigment, and a minorproportion of organic adhesive material or binder, said surface layerbeing deposited from an aqueous medium. Such paper provides an excellentsurface to be printed by conventional printing methods and is quitedistinct from a lacquered or varnished surface which may have equalgloss, but which is usually not printable in the same manner and ofwhich the ingredients and proportions are quite different.

I claim:

1. A mold-nutrient-free supercalendered mineral coated paper soapwrapper comprising a paper base and a mineral coating, said paper baseconsisting essentially of cellulose fibers and said mineral coatingconsisting essentially of finely divided mineral matter, a syntheticadhesive elastomer of the group consisting of styrene- 40 butadienecopolymers, butadiene-acrylonitrile copolymers, styrene-isoprenecopolymers, methyl acrylate-acrylonitrile copolymers and polychloro- 6 1prene and a protective colloid of the group consisting of polyvinylalcohol, methyl cellulose, carboxymethyl cellulose and hydroxyethylcellulose.

2. A mold-nutrient-free supercalendered mineral coated paper soapwrapper as defined in claim 1 in which the cellulose fibers are rosinsized.

3. A mold-nutrient-free supercalendered mineral coated paper soapwrapper as defined in claim 1 in which the paper base contains a mineralfiller.

4. A mold-nutrient-free supercalendered mineral coated paper soapwrapper as defined in claim 1 in which the adhesive elastomer isstyrene-butadiene copolymer.

5. A mold-nutrient-free supercalendered mineral coated paper soapwrapper as defined in claim 1 in which the protective colloid ispolyvinyl alcohol.

6. A mold-nutrient-free supercalendered mineral coated paper soapwrapper as defined in claim 1 in which the adhesive elastomer isstyrene-butadiene copolymer and the protective colloid i polyvinylalcohol.

'7. A mold-nutrient-free supercalendered mineral coated paper soapwrapper as defined in claim 1 in which the cellulose fiber is virgincellulose.

JOSEPH J. THOMAS.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date ,982,018 Owen Nov. 27, 1934 2,267,310 Shearer Dec. 23, 19412,287,348 Hayden June 23, 1942 2,322,887 Schwartz June 29, 1943 ,328,057Coulter Aug. 31, 1943 2,453,880 Vanderbilt Nov. 16, 1948 2,474,801 OwenJune 28, 1949 2,496,566 Szwarc Feb. '7, 1950 2,537,114 Young et a1 Jan.9, 1951 OTHER REFERENCES Partridge, Latex Compounds for Paper Industry,May 1948, pages 221-223, India Rubber World.

1. A MOLD-NUTRIENT-FREE SUPERCALENDERED MINERAL COATED PAPER SOAPWRAPPER COMPRISING A PAPER BASE AND A MINERAL COATING, SAID PAPER BASECONSISTING ESSENTIALLY OF CELLULOSE FIBERS AND SAID MINERAL COATINGCONSISTING ESSENTIALLY OF FINELY DIVIDED MINERAL MATTER, A SYNTHETICADHESIVE ELASTOMER OF THE GROUP CONSISTING OF STYRENEBUTADIENECOPOLYMERS, BUTADIENE-ACRYLONITRILE COPOLYMERS, STYRENE-ISOPRENECOPOLYMERS, METHYL ACRYLATE-ACRYLONITRILE COPOLYMERS AND POLYCHLOROPRENEAND A PROTECTIVE COLLOID OF THE GROUP CONSISTING OF POLYVINYL ALCOHOL,METHYL CELLULOSE, CARBOXYMETHYL CELLULOSE AND HYDROXYETHYL CELLULOSE.